Culture dish



Jan. 15, 1963 .1. GREENBLATT 3,073,750

. CULTURE DISH Filed May 7, 1959 AI'TOBIVEX United States Patent Ofiice Patented Jan. 15, 1963 3,073,750 CULTURE DISH Joseph Greenblatt, pringfield Township, Montgomery (Jonnty, Pa, assignor to Talb Industries, Inc., Philadelphia, Pa., a corporation of Pennsylvania Filed May 7, 1%9, Ser. No. 811,753

3 Claims. (Cl. 195-139) The present invention relates to receptacles for culturing specimens of microorganisms; for example, culture receptacles of the type commonly known as Petri dishes. The invention involves novel structural features and the selection of special materials of construction for such dishes to render the same adaptable and particularly advantageous for certain uses, as will hereinafter appear.

While it has been proposed in certain instances to substitute the glass more commonly employed in Petri dishes by resilient plastics, none of the materials of the plastic type heretofore proposed for such use were found fully satisfactory as a replacement for hard glass. To meet the special needs of the present invention it was necessary to find from among the many kinds of known plastic materials, those that were not only transparent but which in addition could withstand steaming without distortion and which retained sufiicient transparency to enable examination of the contents through the plastic surface after being subjected to such steaming.

Among the desired objects accomplished by the present invention is the provision of a covered culture dish made from a special type of transparent plastic composition capable of withstanding sterilization in flowing steam. Another object is the construction of such dishes in a form such that introduction of the organism to be studied can be effected without removal of the tightly fitting cover.

The culture dish constructed in accordance with the present invention is particularly advantageous for use in field investigations and demonstrations, for example, in comparing efficiency of disinfecting, sterilizing or sanitizing compositions. Such use requires a culture dish of comparatively low cost, capable of being handled, stored or shipped without resort to burdensome precautions against breakage, and one capable of convenient use by persons lacking the training and skills of the laboratory technician in biology or bacteriology.

The above-described and other advantages hereinafter appearing are attained in accordance with the present invention by the use of the particular plastic compositions described below, molded to form a sectionally divided culture dish base and fitted cover therefor, so arranged that each of the sections can be separately inoculated without contamination therebetween and without requiring removal of the cover to do so. The construction and operation of the novel device will be understood and other of its advantages appreciated from the description which follows read in connection with the accompanying drawings, wherein:

FIGURE 1 is a perspective view of the dish and cover in separated position;

FIGURE 2 is a plan view of the dish with cover in lace; p FIGURE 3 is a cross-section through the dish taken along the line 3-3- of FIGURE 2.

The base member of the dish comprises a bottom disk 11 and an upright integrally formed, substantially cylindrical, wall portion 12, arranged a short distance inwardly from the peripheral edge 13 of disk 11, to provide an extending ledge or flange. This ledge or flange is scalloped, fluted or serrated, around its external periphery so as to provide a hand grip. An upright, diametrically extending partition member 14 divides the base of the dish into separated compartments. Although a single partition is shown separating the base into two compartments, 1

it will be understood that a larger number of compartments may be provided, if desired, by utilizing several such partition members intersecting at their midpoints with their ends intercepting the cylindrical wall 12.

Notches or slots 15 are formed in the wall 12; there being a separate notch communicating with each compartment formed in the base 10. The slots 15 do not extend the full distance to the face of disk 11 but stop short thereof so as to provide a rim portion 16 between the bottom of the slot and the upper face of the disk. This rim portion is preferably about to /1 inch in height, in a standard dish which is approximately to /v, inch in height.

The cover member 20 is formed by a top disk 21 and downwardly extending cylindrical wall portion 22 integral therewith and at the extreme periphery thereof. The internal diameter of the cover member is slightly larger than the external diameter of wall 12, so as to fit thereover in easy sliding contact, thereby permitting the wall 22 of the cover to be fitted over the wall 12 as the cover is pushed down over the base until the free edge of wall 22 intersects the top surface of ledge 13. Preferably the wall 12 is made slightly thicker near the bottom thereof, with a gradual downward and outward taper uniformly around the circumference of the portion of wall 12 that is approximately coextensive with the height of rim 16 As the wall 22 of the cover slides over this tapered P I- tion of wall 12, it is forced outward slightly to provide a tight fit, so that the covered dish is substantially impervious to air-borne dust or other particles. Because of the low coefiicient of friction and the yi-eldable nature of the plastic, rotatable sliding movement between the cover and the base of the closed dish can be effected with moderate manual force while holding the base by the friction grip provided by the scalloped edge 13.

The cover 20 is provided with a single notch or slot 23 formed in wall 22 similar to the slots 15 in the base. The slot 23 stops short of the inner surface of disk 21, leaving a rim 24 between the base of the slot and said surface. The slot 23 is substantially of the same size as the slots 15. By rotating the cover 20 on the base 10, the slot 23 can be brought into registry selectively with the several slots 15 as desired. Moreover, by the provision of the slot 23 in wall 22, flexing of the wall is facilitated as the free edge thereof is forced over the thickened portion of wall 12. When the cover 20 is in place over the base to the full extent and the slot 23 is out of registry with any of slots 15, the rim portions 16 and 24 assist in sealing the receptacle at the slotted areas.

The cover 20 is provided at the center of the top thereof with a small knob or protuberance 25, formed by thickening of the material at that point, for purposes hereinafter explained.

To withstanding sterilization by heating in steam without distortion or loss of transparency, the kinds of plastics from which the base and cover can be formed are limited. Of the large number of materials tested satisfactory results were obtained in only few instances. We have found suitable for the described purpose homopolymerized methyl styrene, one form of which is more widely known under the trade name Cymac 400. Also effective, but slightly less water resistant, are the copolymers of methyl styrene with \acrylonitrile. Other plastic materials, represented to be resistant to boil-ing water were not found fully satisfactory for the desired purpose because of their tendency to cloud on steaming, with permanent impairment of transparency. On the other hand, while some clouding does develop even in the case of the preferred methyl styrene products, when subjected to freeflowing steam, the cloud disappears within a few hours at room temperature or incubator temperatures, permitting ready inspection of the contents of the covered dish. The

cover and plate are separately formed by injection or compression molding.

For those uses in which post-sterilization is not required, or in situations wherein such sterilization, if required, can be accomplished by chemical vapors or other treatment which is not detrimental to the nutrient media in the dish, a wider choice of transparent plastic is possible. Also a wider selection of plastics is available if provision is made for the introduction of the nutrient media under aseptic filling conditions. Under these conditions one may employ for production of the culture dishes, plastics made of methyl methacrylate, poly methyl alpha chloro acrylate, polypropylene, or the known heat and chemical resistant styrene molding compounds.

For the suggested use of the novel culture dish in a field kit, the dish containing both compartments filled to proper level with nutrient media, will be packaged together with ampules containing sterile swabs for obtaining smears of a test area. In use, it is then only necessary for the operator to wipe one of the sterile swabs over an area to be tested and smear the speciment lightly over the layer of nutrient agar in one of the compartments of the dish, inserting the swab through the opening in the side of the dish provided by rotating the cover plate until the slot 23 therein coincides with the slot of the selected compartment. After removing the swab, the cover is given a slight turn to reseal the covered dish. In the same way the other compartment may be inoculated with a control or with another specimen, using a separate sterile swab to wipe the test area, and inserting that swab into the opposite compartment through the opening in the side of the dish provided by rotating the cover until the slot therein coincides with the other slot 15 in the base. By now backing off about a quarter turn, the covered dish is again sealed. In a typical case growth of the organisms will be developed by about two days storage at room temperature, or if facilities are available incubation at somewhat higher temperature may be employed to accelerate development. The growths obtained in the several compartments can be examined through the top or the bottom of the dish without requiring removal of the cover. If desired to preserve the specimens in that form without further growth, the organisms can be killed by introducing a few drops of formaldehyde through the respective openings in the sides and rescaling the dish by appropriate rotation of the cover.

The dishes may be sterilized before filling with the agar or other selected media, by exposure to ethylene oxide or to ultraviolet light. If the filling of the compartments is carried out under aseptic conditions, further sterilization may not be needed. By the use of the special plastic compositions hereinbefore described which are capable of withstanding steam treatment, there is no need to resort to the inconvenience of aseptic filling. After introduction of the culture media, the filled dishes can be exposed to free-flowing steam for one hour or more. To assure sterility the steaming should be repeated after 24 hours. The slight cloud which may appear on steaming will disappear after a few hours at room temperature or in mild dry heat.

It has been found in practice that by the provision of the protuberance 25, the strain on the plastic as a result of the slight expansion due to steaming and subsequent contraction on cooling, is relieved to sufiicient extent to reduce materially any binding tendency between the walls 12 and 22. While the action of the protuberance in this manner cannot be fully explained, it has been found that the dishes provided with fitted covers made in this manner, permit easy rotation of the cover with only moderate force after exposure to the steam treatment, whereas in the case of similarly prepared dishes having covers not provided with the protuberance, there was often considerable binding between the cover and the base, rendering relative rotation quite difficult.

While for the special uses indicated culture dishes made of plastic are preferred, it will be understood that certain of the features of the invention can be advantageously adopted in dishes made of glass or other materials.

Obviously many modifications and variations of the present invention as hereinbefore set forth may be made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

What is claimed is:

l. A covered culture dish made of transparent steamresistant and heat-resistant plastic, said dish comprising:

(a) a base member provided with a circumferential wall and being partitioned to provide separate compartments in said base member;

(6) a layer of active nutrient gel media in sterile condition in each of said compartments, the atmosphere within said dish above said layer being also sterile;

(c) a tightly-fitting cover member having a circumferential wall which in closed position tightly overlaps the wall of said base member, while permitting sliding and rotational movement therebetween;

(d) a plurality of slots formed in the wall of said base member at opposite sides thereof;

(e) the circumferential wall of said base member being outwardly and downwardly tapered, at least near the bottom thereof, to provide a tight seal with said cover member when overlapping said tapered portion, rendering the dish in such overlapping position impervious to air-borne dust and other particles;

(f) a slot formed in the wall of said cover member facilitating flexing of the wall of said cover member as the wall of said cover member is forced down over the tapered wall of said base member in sealing position, whereby rotation of said cover member relative to said base member brings the slot in said cover member into registry respectively with each of the slots in the base member to provide a temporary opening into the covered dish, through which an implement can be inserted for separate inoculation of the nutrient layer in each of said compartments;

(g) said base member being further provided with a ledge extending outwardly of the circumferential wall thereof, and said ledge being fluted to provide a hand group on said base member to facilitate manual relative rotation between said base member and said cover member.

2. A culture dish as defined in claim 1 wherein said cover member is provided with a central protuberance formed by thickening of the material at that point.

3. A culture dish as defined in claim 1, wherein said plastic is a homopolymer of methyl styrene.

References Cited in the tile of this patent UNITED STATES PATENTS 2,144,255 Carpenter July 17, 1939 2,677,646 Lovell et al May 4, 1954 2,677,647 Lovell May 4, 1954 2,745,824 Melchone May 15, 1956 2,774,466 Liska Dec. 18, 1956 2,851,447 Wesp et al. Sept. 9, 1958 2,874,091 Fisk Feb. 17, 1959 

1. A COVERED CULTURE DISH MADE OF TRANSPARENT STEAMRESISTANT AND HEAT-RESISTANT PLASITIC, SAID DISH COMPRISING: (A) A BASE MEMBER PROVIDED WITH A CIRCUMFERENTIAL WALL AND BEING PARTITIONED TO PROVIDE SEPARATE COMPARTMENTS IN SAID BASE MEMBER; (B) A LAYER OF ACTIVE NUTRIENT GEL MEDIA IN STERILE CONDITION IN EACH OF SAID COMPARTMENTS, THE ATMOSPHERE WITHIN SAID DISH ABOVE SAID LAYER BEING ALSO STERILE; (C) A TIGHTLY-FITTING COVER MEMBER HAVING A CIRCUMFERENTIAL WALL WHICH IN CLOSED POSITION TIGHTLY OVERLAPS THE WALL OF SAID BASE MEMBER, WHILE PERMITTING SLIDING AND RATIONAL MOVEMENT THEREBETWEEN; (D) A PLURALITY OF SLOTS FORMED IN THE WALL OF SAID BASE MEMBER AT OPPOSITE SIDES THEREOF; (E) THE CIRCUMFERENTIAL WALL OF SAID BASE MEMBER BEING OUTWARDLY AND DOWNWARDLY TAPERED, AT LEAST NEAR THE BOTTOM THEREOF, TO PROVIDE A TIGHT SEAL WITH SAID COVER MEMBER WHEN OVERLAPING SAID TAPERED PORTION, RENDERING THE DISH IN SUCH OVERLAPPING POSITION IMPERVIOUS TO AIR-BORNE DUST AND OTHER PARTICLES; (F) A SLOT FORMED IN THE WALL OF SAID COVER MEMBER FACILITATING FLEXING OF THE WALL OF SAID COVER MEMBER AS THE WALL OF SAID COVER MEMBER IS FORCED DOWN OVER THE TAPERED WALL OF SAID BASE MEMBER IN SEALING POSITION, WHEREBY ROTATION OF SAID COVER MEMBER RELATIVE TO SAID BASE MEMBER BRINGS THE SLOT IN SAID COVER MEMBER INTO REGISTRY RESPECTIVELY WITH EACH OF THE SLOTS IN THE BASE MEMBER TO PROVIDE A TEMPORARY OPENING INTO THE COVERED DISH, THROUGH WHICH AN IMPLEMENT CAN BE INSERTED FOR SEPARATE INOCULATION OF THE NUTRIENT LAYER IN EACH OF SAID COMPARTMENTS; (G) SAID BASE MEMBER BEING FURTHER PROVIDED WITH A LEDGE EXTENDING OUTWARDLY OF THE CIRCUMFERENTIAL WALL THEREOF, AND SAID LEDGE BEING FLUTED TO PROVIDE A HAND GROUP ON SAID BASE MEMBER TO FACILITATE MANUAL RELATIVE ROTATION BETWEEN SAID BASE MEMBER AND SAID COVER MEMBER. 